The size of electronic devices ranges from the very small to the very large. Gaming devices, portable data assistants (PDAs) and other portable computing devices, laptops, cell phone, smart phones, video players, music players, medical devices, and numerous other types of electronic devices are typically provided in sizes and shapes that are convenient for a user to hold, carry, and transport, for example, by being able to fit within a user's purse or pocket. For example, portable electronic devices are beginning to be used as personal computing platforms, combining computational power and communication capabilities with user convenience in a compact form. Typically such devices include a display used to present pertinent information to the user and, in some cases, the display surface can also be used as a touch sensitive input device. A popular form of such a portable electronic device fits comfortably in a shirt pocket.
Thin flat flexible sheets may be used as substrates for displays of electronic devices. For example, polyester (PET and PEN) films are available in many thicknesses such as 25 micrometers (1 mil) to 250 micrometers (10 mils). These films are flexible; for example they bend under gravity when draped over a shaped object.
Adding curvature to the geometry of a sheet makes it behave like a shell. A shell carries loads through a combination of “membrane response” and bending response. Membrane response or “shell response” can cause a shell to become relatively stiff.
Examples of curved shells include arched panels and cylindrical pipes. An egg shell also provides a good example of strength and response of a curved shell. When loaded primarily in “membrane mode” the egg shell is very strong. However, if loaded locally in bending, the load capacity is low and the shell may break.
Sputtered thin films of metal alloys comprising titanium and nickel known as NITINOL are capable of achieving high recoverable stresses of the order of 350 MPa, while having fatigue performance corresponding to thousands of cycles of actuation for the case of strain of approximately 3% or less, as described by Krulevitch et. al. New methods for fabricating thin film NITINOL at an attractive cost are under development, for example using Chemical Vapor Deposition, CVD.
Tantalum nitride (TaN) thin film resistors are rugged and stable; they have a typical sheet resistance of 100 ohms per square and good power-handling capabilities, as described by Licari et. al.
Despite the progress made in the displays and other components of electronic devices, there is a need in the art for improved devices and methods of making such devices.